The present invention relates to a developing apparatus, a process cartridge and an image forming apparatus.
In an image forming apparatus such as a laser printer, an electrostatic latent image is formed on the surface of a photoconductor drum and developer is supplied to the electrostatic latent image from a developing apparatus, so that a developer image is retained on the surface of the photoconductor drum. The developer image is then transferred to a paper sheet, so that formation of an image on the paper sheet is achieved.
A developing apparatus comprises: a case having an opening faced to the photoconductor drum; a developer retainer for retaining developer which is held in the case; and a blade for regulating the layer thickness of developer to be retained by the developer retainer. The developer retainer is supported so as to be rotatable with a portion of the surface thereof being exposed at the opening of the case. The blade is composed of a sheet-like elastic blade extending in the axial direction of the developer retainer and a support plate for supporting this elastic blade. The elastic blade has an upper end portion, which is welded to the support plate by spot welding at constant intervals (10 mm, for example) in the longitudinal direction, and a lower end portion, which is welded to the surface of the developer retainer by pressure welding, so as to press the developer retainer uniformly in the longitudinal direction. (See Japanese Patent Application Laid-Open No. 2001-356592, for example). The developer in the case is supplied onto the surface of the developer retainer, carried between the blade and the surface of the developer retainer with the rotation of the developer retainer and retained on the surface of the developer retainer as a thin layer having a constant thickness. The developer retained on the surface of the developer retainer is supplied to the electrostatic latent image formed on the surface of the photoconductor drum when the developer comes in contact with the surface of the photoconductor drum.
Such a developing apparatus is usually provided with sealing members for preventing leakage of toner from the longitudinal end portions of the developer retainer. The sealing members are arranged adjacent to the longitudinal end portions of the developer retainer and pressed to the surface of the longitudinal end portions of the developer retainer. Suggested is, for example, to compose such a sealing member of an upstream sealing member and a downstream sealing member having different elasticity, arrange the upstream sealing member having larger elasticity on the upstream side in the rotative direction of the developer retainer and arrange the downstream sealing member having smaller elasticity on the downstream side (see Japanese Patent Application Laid-Open No. H11-73017/1999, for example).